MSPs have quietly awarded themselves an increase in expenses, even before a controversial new scheme is debated, it emerged today.

A report by an independent panel earlier this year proposed an overhaul of allowances, including a plan to give constituency MSPs £62,000 a year for staff costs while their regional list colleagues would receive £45,000 because of a supposedly lighter workload.

The Scottish Parliament will vote on the panel's recommendations tomorrow. It is expected to agree to give all MSPs the same level of staff allowance.

But because the panel's report was published in March, before the start of the new financial year, the cross-party Scottish Parliamentary Corporate Body has taken the opportunity to increase all the amounts by inflation.

The proposal to be put to the parliament tomorrow now includes staff allowances of £64,300 for constituency MSPs and £46,700 for list members.

The amendment likely to be passed by MSPs to equalise the allowance will also be based on an "uprated" figure. That would give all MSPs a staff allowance of around £56,600.

A senior Labour MSP said: "This is a back-door increase. Everyone has been talking about the figures set out in the report and then suddenly we find they have been uprated."

The proposed levels of other allowances have also been increased. The maximum annual amount that can be claimed for overnight accommodation in Edinburgh has gone up from £11,400 to £11,900. The annual limit on office costs has risen from £15,000 to £15,600, and the maximum claim allowed for surgery advertising costs has increased from £1500 a year to £1560 a year.

The move to ensure all MSPs receive the same staff allowance is expected to be backed by the SNP, the Tories, the Greens and independent Lothians MSP Margo MacDonald – which should be enough to ensure it wins.

The Liberal Democrats are likely to have a free vote, leaving only Labour backing the differential proposed by the panel, chaired by Dundee University principal Sir Alan Langlands.

Labour chief whip Jackie Baillie said the party preferred to support the recommendations of an independent review rather than a "backroom fix" drawn up by politicians.

She hinted that Labour was also considering trying to block the uprating of the allowances.

She said: "Our position has always been Langlands as it is. We never anticipated that Langlands would be uprated."

But one parliament source defended the uprating as only following the panel's recommendations. He said: "The Langlands report was received before April 1, but he concluded the rates should be uprated every year."